Proposed is a method for accurately predicting an overcurrent flowing inside an isolated bidirectional DC-DC converter even without using a current sensor on primary and secondary sides of a transformer. In the converter according to the present disclosure, an average value of the inductor current is calculated after deriving inflection point current values by respectively modeling a current waveform for an inductor current of the transformer. A secondary side output current average value is calculated by comparing the calculated average value of the inductor current with a secondary side capacitor current average value of the converter at no load. Next, an error between the secondary side output current average value and an actually measured secondary side output current is calculated, and the inflection point current values of the current waveform are updated using a gain for reducing the error through PI control, whereby the overcurrent may be predicted.
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2. The method of claim 1, wherein the modeled inductor current increases or decreases linearly, has the average of zero within one period, and is formed such that an element for a first half period x and an element for a second half period x are identical except having opposite signs.
3. The method of claim 1, wherein the plurality of input values comprises a peak value (Vpri) of a primary side voltage of the transformer, each frequency (ωsw) of switching frequencies of the first and second switching units, an internal equivalent inductance (L) of the converter, a zero period length (a) of the primary side voltage of the transformer, a zero period length (β) of a secondary side voltage of the transformer, a phase difference (φ) between the primary and secondary side voltages of the transformer, and a voltage ratio (g) between the primary and secondary side voltages of the transformer.
7. The method of claim 6, wherein, when the updated inflection point current value is greater than a preset reference value, the predicting an overcurrent predicts the overcurrent has occurred.
8. The method of claim 3, wherein, in the step-down condition, the current waveform is characterized that, in the case of φ≥0, the Vpri has a phase faster than the Vsec by the φ, and the Vsec is smaller than the Vpri, and in the case of φ<0, the Vpri has the phase delayed more than the Vsec by the φ, and the Vsec is smaller than the Vpri.
9. The method of claim 3, wherein, in the step-up condition, in the case of φ≥β>0, the Vpri has a phase faster than the Vsec by the φ, and the Vsec is greater than the Vpri, and in the case of φ<β, the Vpri has the phase faster than the Vsec by the φ, and the Vsec is greater than Vpri.
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December 30, 2020
November 12, 2024
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